Electromagnetic metering valve for a fuel injector

ABSTRACT

A metering valve presenting a shutter for a discharge conduit, and an  eleomagnet in turn presenting a fixed core and a disk-shaped armature detached from and sliding on the stem by means of a sleeve. The stem is guided by a bush, presents a flange movable inside a swirl chamber with a velocity damping effect, and is fitted, prior to assembling the armature and the electromagnet, by means of a ring nut, which presses a flange, forming one piece with the bush, against the body of the valve via the interposition of calibrated washers so selected as to define the travel of the stem.

BACKGROUND OF THE INVENTION

The present invention relates to an improved electromagnetic meteringvalve for a fuel injector, in particular for internal combustionengines.

The metering valves of fuel injectors normally comprise a controlchamber with a discharge conduit, which is normally kept closed by ashutter. In known metering valves, the shutter is normally kept closedby the armature of an electromagnet, with the aid of a spring, and isreleased to open the conduit by energizing the electromagnet to move thearmature towards the core of the electromagnet.

The armature of known valves is normally connected rigidly to a stemsliding in a guide, and, when closing the discharge conduit, the kineticenergy of the armature and stem is dissipated in the impact of theshutter against the valve. More specifically, in the case of a ballshutter, the kinetic energy is dissipated, via a guide plate and theball, in the impact against the seat in the valve body. Conversely, whenopening the discharge conduit, the kinetic energy due to the returnmovement of the armature and stem is dissipated in the impact of thestem against a stop.

Such impact generates considerable force, which is proportional to themass and velocity of the armature and stem, and is inverselyproportional to impact time, which is very short. Owing to the hardnessof the ball and valve body, the impact when closing the valve results inconsiderable rebound, which is also generated, when opening the valve,by the impact of the stem against the stop. As such, the movement of thearmature, and hence the opening and closing movement of the valve, failsto provide for steady operation of the injector.

Moreover, the armature moves inside a fuel discharge chamber in whichthe pressure and density of the fuel vary considerably. An increase inthe pressure, and hence in the density, of the fuel inside the dischargechamber reduces the velocity of the armature both when opening andclosing the valve. Finally, the movement of the armature itselfproduces, and is seriously affected by, pressure waves in the fuelinside the discharge chamber, thus further impairing steady operation ofthe injector.

A metering valve has been proposed wherein the armature is made ofmagnetic material; the stem is made of nonmagnetic material to reducecost, and is detached from the armature to simplify assembly; and thestem is guided by a sleeve forming one piece with a bell fixed to theinjector body, so that the stem is arrested by a very small surface andsubject to rebound.

Moreover, the armature, stem and guide are assembled together with theelectromagnet, so that the travel of the stem cannot be determinedwithout also assembling the armature and the electromagnet, and cannotbe measured easily for test purposes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a highlystraightforward, reliable metering valve of the above type, designed toovercome the aforementioned drawbacks typically associated with knowndevices, and which provides for perfectly steady operation of theinjector.

According to the present invention, there is provided a metering valvecomprising a shutter for a discharge conduit of a control chamber of aninjector; and an electromagnet presenting a fixed magnetic core and amovable armature for controlling said shutter; said armature acting onsaid shutter by means of an element normally pushed elastically to keepsaid shutter in a position wherein said conduit is closed; and saidelement being guided by guide and travel arresting means; characterizedin that said element comprises a portion housed in a swirl chambercommunicating with a discharge chamber; said portion presenting asurface which is arrested against said means and such that the openingmovement of said element is dampened by rapid compression and expulsionof the fluid in said swirl chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Two preferred non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a partly sectioned view of a fuel injector incorporating ametering valve in accordance with the present invention;

FIG. 2 shows a larger-scale section of the metering valve of the FIG. 1injector.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, number 5 indicates a fuel injector, e.g. for adiesel engine, comprising a hollow body 6 in which slides a control rod8, and which is connected at the bottom to a nozzle 9 terminating withone or more injection orifices 11.

Body 6 also presents an appendix 13 in which is inserted an inletfitting 16 connected to a standard high-pressure fuel supply pump. Bymeans of conduits 17, 18 and 21 (FIG. 1), a hole 14 (FIG. 2) in appendix13 communicates with an injection chamber 19 of nozzle 9; orifice 11 isnormally kept closed by a pin 28 connected to rod 8 by a plate 100; pin28 presents a shoulder 29 on which the pressurized fuel in chamber 19acts; and a compression spring 37 assists in pushing plate 100 and hencepin 28 downwards.

Injector 5 also comprises a metering valve 40 comprising a sleeve 41(FIG. 2) supporting an electromagnet 42 for controlling a disk-shapedarmature 43. Sleeve 41 is fitted to body 6 by means of a thread 44 whichscrews on to an external thread of body 6, and sleeve 41 presents ashoulder 45 on which rests a magnetic core 46 of electromagnet 42.Between the bottom edge of sleeve 41 and a shoulder 38 of body 6, thereare fitted a number of calibrated washers 39 so selected as to definethe axial position of core 46 at a predetermined distance from the topsurface of disk 43.

Core 46 is annular and presents a central hole 49; an annular seat 48 ofcore 46 houses a standard electric coil 47 for activating electromagnet42; sleeve 41 presents a bent edge 50 connecting core 46 to a disk 52forming one piece with a discharge fitting 53 coaxial with hole 49 andconnected to the fuel tank; and a cover 54 made of insulating materialand fitted with a standard pin 55 of coil 47 is co-molded in knownmanner on to sleeve 41.

Metering valve 40 also comprises a body 56 presenting a flange 57, whichis normally kept contacting a shoulder 58 of body 6 of the injector by aring nut 59; ring nut 59 is threaded externally and screwed on to athread of a discharge chamber 60 formed in body 6 as explained in moredetail later on; and chamber 60 extends axially from the top surface ofbody ring nut 59 of valve 40 to the bottom surface of core 46.

Body 56 of valve 40 also presents an axial control chamber 61communicating with a calibrated radial inlet conduit 62, and with acalibrated axial discharge conduit 63; inlet conduit 62 communicateswith hole 14; control chamber 61 is defined at the bottom by the topsurface of rod 8; and, by virtue of the greater area of the top surfaceof rod 8 as compared with that of shoulder 29 (FIG. 1), the pressure ofthe fuel, with the aid of spring 37, normally keeps rod 8 in such aposition as to close orifice 11 of nozzle 9.

Discharge conduit 63 of control chamber 61 is normally kept closed by ashutter in the form of a ball 67, which rests in a conical seat formedby the plane of contact "X" with conduit 63. Ball 67 is guided by aguide plate 68 on which acts a stem 69 associated with disk 43; and disk43 forms one piece with a sleeve 71 sliding axially on stem 69, presentsa shoulder 72 engaged by an open ring 73 fitted inside a groove 74 onstem 69, and presents slots 76 to improve the armature magnetically andhydrodynamically and to assist fuel flow from chamber 60 to central hole49 of core 46.

Stem 69 extends a given length inside hole 49, and terminates with asmall-diameter portion 77, which provides for supporting and anchoring afirst compression spring 78 housed inside hole 49, between stem 69 anddisk 52. A second compression spring 79, of much greater flexibilitythan spring 78, i.e. having a much weaker force than spring 78, isfitted between disk 43 and ring nut 59, and normally keeps disk 43resting on open ring 73 of stem 69. It should be pointed out that disk43 moves inside an ample portion "A" of discharge chamber 60--which isnormally full of air-fuel mixture--and therefore generates pressurewaves.

Stem 69 slides inside a guide 82 comprising a cylindrical bush 83, and abottom flange 84 presenting axial holes 86; flange 84 is forced by ringnut 59 against flange 57 of body 56 of valve 40 with the interpositionof calibrated washers 87 so selected as to define the travel "h" of stem69; and stem 69 presents an integral bottom flange 88 with aconsiderable surface "S" by which stem 69 is arrested against the bottomsurface "Y" of flange 84.

Flange 88 of stem 69 is housed inside a swirl or "squish" chamber 89 inwhich the fluid between surface "S" of flange 88 and the correspondingsurface "Y" of flange 84 is compressed between said surfaces (S and Y)to dampen the movement of stem 69 and disk 43 ("squish" effect). Bush 83and ring nut 59 form a gap 91 enabling the fluid to flow from chamber 89through holes 86 into discharge chamber 60.

Ring nut 59 locks washers 87, guide 82 of stem 69 and body 56 ofmetering valve 40 to injector body 6, which is deformed elastically bythe axial force generated by the tightening torque of ring nut 59. Whenbody 56 is subjected to high pressure in chamber 61, the axial forceopposes that generated by the tightening torque to restore the elasticdeformation of body 6. Since ring nut 59 locks both guide 82 and body 56of valve 40, however, said elastic deformation in no way affects themutual position of plane "X" and surface "Y", so that there is novariation in travel "h" of stem 69.

Metering valve 40 of injector 5 operates as follows.

When coil 47 is energized, core 46 attracts disk 43 which, by means ofshoulder 72 and ring 73, positively raises stem 69 in opposition tospring 78; and flange 88 of stem 69 generates inside swirl chamber 89 aswirling or squish effect by which the fluid in chamber 89 is compressedand expelled to dampen the stoppage of stem 69 and so prevent reboundand provide for steadier operation of metering valve 40 and injector 5.

Though stem 69 is arrested with flange 88 against the surface of flange84 of guide 82, and disk 43 is arrested with shoulder 72 against ring73, the respective kinetic energies are absorbed separately by virtue ofdisk 43 being detached from stem 69. Since disk 43 moves in portion "A"of chamber 60, its movement is also slowed, thus further reducing thekinetic energy to be absorbed, while the variation in pressure inportion "A" in no way affects the movement of stem 69.

The pressure of the fuel in chamber 61 therefore opens shutter 67 todischarge the fuel in chamber 60, which is fed back to the tank; and thepressure of the fuel in chamber 19 (FIG. 1) acts on shoulder 29 of pin28 to raise pin 28 and inject the fuel in chamber 19 through orifice 11.

When coil 47 (FIG. 2) is de-energized, spring 78 pushes down stem 69,which, via ring 73, lowers disk 43; the kinetic energy of disk 43 isdissipated by spring 79 independently of that of stem 69; and thekinetic energy of stem 69 is partly dissipated by the swirling or"squish" effect generated by flange 88 in the fluid inside chamber 89.

As a result, the impact of stem 69 on plate 68, of plate 68 on ball 67,and of ball 67 on the seat in discharge conduit 63, is greatly reducedwith substantially no rebound; ball 67 closes discharge conduit 63; thepressurized fuel restores the pressure inside control chamber 61; andpin 28 (FIG. 1) closes orifice 11.

The structure of metering valve 40 also provides for defining and/ormeasuring the travel "h" of stem 69 without assembling core 46 or disk43 to body 6. Travel "h" in fact is defined by appropriately selectingand fitting calibrated washers 87 between body 56 of valve 40 and guide82 of stem 69 by means of ring nut 59. At which point, spring 79 andsleeve 71 are fitted on to stem 69, and disk 43 is locked in place byinserting open ring 73 inside groove 74.

Since stem 69 at this point is maintained contacting guide 82 by spring79 and disk 43, the travel "h" of stem 69 is measured by simply placingthe end of a normal travel gauge on the top end of portion 77 of stem69, and moving stem 69 until ball 67 contacts its seat. Finally, body 6is closed by assembling sleeve 41 fitted beforehand with disk 52,electromagnet 42 and spring 78.

The advantages of metering valve 40 will be clear from the foregoingdescription. In particular, stop surface "S" of flange 88 and the"squish" effect provide for eliminating rebound of stem 69 both whenopening and closing shutter 67; the fact that disk 43 is detached fromstem 69 reduces the kinetic energy to be dissipated by stem 69 onstriking flange 84 and on ball 67 striking its seat; and the arrangementof guide 82 and stem 69 enables the travel of stem 69 to be definedand/or measured without assembling electromagnet 42.

Clearly, changes may be made to the metering valve as described andillustrated herein without, however, departing from the scope of thepresent invention.

I claim:
 1. An electromagnetic metering valve for a fuel injector,comprising a control chamber (61) supplied with fuel under pressure, adischarge conduit (63) for discharging the fuel of said control chamber(61), a shutter (67) for said discharge conduit (63), a dischargechamber (60) communicating with said conduit (63), and an electromagnet(42) presenting a fixed magnetic core (46) and a movable armature (43)for controlling said shutter (67); said armature (43) being associatedwith a stem (69) provided with a first flange (88) for controlling saidshutter (67), a first spring (78) normally pushing said stem (69) with apredetermined force to keep said shutter (67) in a position closing saiddischarge conduit (63); said stem (69) being guided by stationary guideand travel arresting means (82), wherein said first flange (88) isprovided with a first surface (S), and said guide and travel arrestingmeans (82) comprise a bush (83) slidably guiding said stem (69), and asecond flange (84) fitted to a body (56) of the valve; said secondflange (84) being provided with a second surface (Y) adapted to beengaged by the first surface (S) to arrest said first flange (88), saidsecond flange (84) defining a swirl chamber (89) located between saiddischarge conduit (63) and said discharge chamber (60) and housing saidfirst flange (88), wherein an opening movement of said first flange (88)is dampened by rapid compression and expulsion of the fuel in said swirlchamber (89) between said first surface (S) and said second surface (Y).2. The valve as claimed in claim 1, characterized in that said flange(84) is forced against said body (56) by a threaded ring nut (59)cooperating with a thread of a body (6) of the injector, so that thedistance (h) between said corresponding surface (Y) and a plane ofcontact (X) of said shutter (67) with said discharge conduit (63) isunaffected by the forcing of said ring nut (59).
 3. The valve as claimedin claim 2, characterized in that said first spring (78) is locatedinside said core (46), between said stem (69) and a fixed member (52);said second spring (79) being located between said disk (43) and saidring nut (59).
 4. The valve as claimed in claim 2, characterized in thatsaid bush (83) is fixed by said threaded ring nut (59) via theinterposition of calibrated washers (87) prior to assembling said disk(43) and said electromagnet (42); said washers (87) being so selected asto achieve a predetermined travel (h) of said stem (69).
 5. The valve asclaimed in claim 1, wherein said core (46) is annular, said armature isin form of a disk (43) integral with a sleeve (71), and said stem (69)is perpendicular to said disk (43) and detached therefrom, said stem(69) being slidable inside said sleeve (71) and being provided with ashoulder (72) adapted to arrest said disk (43), said disk (43) beingurged by a second spring (79) having a weaker force than said firstspring (78) and being movable within a portion (A) of said dischargechamber (60), which is so ample that rebound of said disk (43) whenarrested and variations in the conditions of the fuel in said dischargechamber (60) have a negligible effect on the movement of said stem (69).6. The valve as claimed in claim 5, characterized in that said stem (69)arrests said disk (43) by means of an open ring (73) inserted inside agroove (74) on said stem (69).
 7. The valve as claimed in claim 6,characterized in that said electromagnet (42) and said fixed member (52)are fitted to a sleeve (41) presenting a thread (44) which is screwed toan external thread of said body (6) of the injector via theinterposition of further calibrated washers (39) so selected as todefine the position of said core (46) in relation to said stem (69).